1. Field of the Invention
The invention relates to a method and apparatus for performing trimming or center cutting operations by a mining machine or the like.
2. Summary of the Prior Art
While the cutting chain of the present invention may have many applications, for purposes of an exemplary showing the chain will be described in its use as a trim chain for a non-oscillating, drum type mining machine.
Non-oscillating drum type mining machines have been in extensive use. Briefly, such machines generally comprise a self-propelled vehicle having a centrally located conveyor means for the material being mined. At the forward end of the machine, one or more movable beams support a horizontally oriented drum. The drum mounts a plurality of cutting tools on its periphery. Frequently, the cutting tools are oriented on the drum in a pattern comprising two oppositely oriented helices which are directed towards the center of the drum. This aids in conducting the cut material toward the center of the machine and the aforementioned conveyor.
Through appropriate drive mechanism and gearing, in association with the beam or beams, the drum is caused to rotate about its axis to produce a cutting action. At the position or positions where the drum is supported on one or more of the beams, the drum surface must be interrupted and cannot carry cutting tools. Therefore, one or more trim chains are required to fill in or overlap the one or more portions of the drum not provided with cutting tools.
Such trim chains are of closed loop configuration and, by virtue of the massive construction of such mining machines, it will be understood that the trim chains will have to be a considerable width. As a consequence, such trim chains usually carry a plurality of cutting tools oriented in staggered rows extending the width of the chain. See for example, U.S. Pat. No. 3,679,265.
In usual practice, the mining machine is moved into the face of the material being cut with the cutting drum positioned at the top of the face. Thereafter, through the agency of the beam or beams, the rotating cutting drum is caused to move downwardly, making a complete vertical cut at the face of the material. This procedure is then repeated and the mine entry is thereby advanced.
Heretofore, the aforementioned trim chains comprised a plurality of chain links which were pivotally interconnected together. Selected ones of said links were designed to accommodate cutting tools which were in the general shape of a rod with a pointed hardened end and were positioned on the links in a forwardly and angularly outwardly projecting direction relative to the external surface of the cutting chain so as to effect a cutting action on the face being mined. The maintenance of a specific angular position of the cutting tools relative to the face being mined is quite important.
The chain links were pivotally connected in such manner as to provide at least two axially spaced circles of openings to receive sprocket teeth. At least two axially spaced rows of sprocket teeth were secured to the central portions of the cutting drum and these teeth cooperated with the openings between the links of the cutting chain to impart a driving force to the cutting chain.
Heretofore, it was believed that the length dimension of the teeth of the sprocket and the pitch of the sprocket teeth should closely conform to the length of the chain openings and the pitch of the chain openings so that all of the sprocket teeth engaged in the openings would be imparting a driving force to the chain. It was believed that this would minimize the wear on the sprocket teeth and the chain and hence resulted in this configuration being essentially an industry standard.
With such standard configuration of the sprocket teeth and the chain link openings, it often happened that, due to wear, the driving force was imparted to the cutting chain more by the sprocket teeth entering the chain links than by the sprocket teeth approaching their exit point from the chain links. Due to the resistance to forward movement of the cutting chain resulting from the reaction forces on the cutting tools, the links carrying the cutting tools would be literally pushed away from the base of the sprocket and assume an angle different from that believed to be the optimum cutting angle. Moreover, since the chain links had internal surfaces conformed to snugly engage cylindrical surfaces on the sprockets intermediate the sprocket teeth, this would normally add a frictional driving force from the sprockets to the cutting chain. However, the bunching up or compression of the links of the cutting chain would move the internal link surfaces out of snug engagement with the cylindrical sprocket surfaces faces and hence impose a substantially greater force on the sprocket teeth that were doing the driving of the cutting chain. For this reason, the operation and useful life of cutting chains as heretofore designed and constructed has not been completely satisfactory.